During nighttime driving of a vehicle on a road, the vehicle generally switches between low beams and high beams appropriately, depending on the environment. In the nighttime driving, the vehicle illuminates the area ahead of the vehicle by using mainly low beams. Low beams illuminate the area ahead of the vehicle with a predetermined pattern of light distribution. “To illuminate” is to shine the front area with projected light. A “predetermined” means “determined in advance”. The predetermined light distribution pattern is stipulated in road traffic rules and the like, for example. These road traffic rules and the like are established in each country or in each region. For example, in Japan, low beams are set to illuminate an area 40 meters ahead with such a slightly downward optical axis that oncoming vehicle and preceding vehicle are not dazzled. Low beams are used mainly in driving in city areas.
On the other hand, high beams illuminate a long range on the surface of the road. For high beams, a nearly horizontal optical axis is set with respect to the surface of the road so as to ensure the maximum front visibility during nighttime driving. In other words, the rays of high beams are thrown parallel to the surface of the road. High beams can illuminate a range up to 100 meters ahead at least. In short, high beams illuminate a wider range ahead of the vehicle with a higher illumination intensity than low beams.
Accordingly, when high beams are used, the visibility of the driver is improved. High beams, however, dazzle the driver of a vehicle running ahead of the vehicle, the driver of an oncoming vehicle, pedestrians ahead of the vehicle, and the like. Therefore, driving with high beams is permitted only when people ahead of the vehicle are not dazzled.
To solve those problems caused by driving with high beams, a technology of changing the light distribution of high beams has been proposed. In other words, a technology for solving the problem of dazzling people ahead of the vehicle has been suggested. The “light distribution” here is the luminous intensity distribution of a light source with respect to space, namely the spatial distribution of light emitted from the light source.
As a technology for changing the light distribution of high beams, patent reference 1 discloses a headlight, which will be described below. The configuration of the headlight of patent reference 1 is a projector type, including a reflector and a plurality of light source units. A lighting tool unit disclosed in patent reference 1 has a plurality of light distribution patterns in the horizontal direction. The “horizontal direction” is a direction parallel to the surface of the road.
The light source unit includes a light emitting element and a light guiding member having a rectangular front-end outgoing opening. Adjacent light guiding members have a boundary part.
The lighting tool unit controls turning on and turning off of the light source unit corresponding to an individual light distribution pattern. Accordingly, the lighting tool unit can control illumination and non-illumination of an arbitrary light distribution pattern, among a plurality of light distribution patterns. The “non-illumination” is not to throw light.
In short, the lighting tool unit can cease from illuminating a light distribution pattern in a range that can dazzle people ahead of the vehicle, out of the plurality of light distribution patterns, for example. Accordingly, the lighting tool unit can suppress the dazzling of people ahead of the vehicle and can improve the visibility of the driver.